OK, I live in So Cal, went to college up in San Fran, have visited Yosemite numerous times, and have driven CA1 up through Hearst Castle.

If you want to spend a few nights in San Fran, I suggest flying into San Francisco and spending a few days there. Next, drive from there to Yosemite and spend your time in Yosemite. Two options from here:

If you like wine and good food, drive from here to Santa Barbara via the 41 - 99 - 5 - 126. It's kind of a long drive, but it's worth it if you want to spend a few days here.

If you dont care for a "wine country" experience, drive the 41 - 99 - 166 or 58 to the 101. Here, you can spend the night in Santa Maria or San Luis Obispo. The best part of the "coast drive" you are talking about is betwene San Luis Obispo and San Fran anyway (and San Luis Obispo is an awesome city).

No matter what, plan on 3 days to drive up the coast (to enjoy all the sights and everything).

Fly out of SFO.

Best time to do this itinerary is September or October, hands down. We have something called "June gloom" here in California - coastal clouds can be socked in for days at a time in May and June. April may be doable, but you chance rain. September or October can be warm, but thats what you come to Cali for, right?

So, it looks as if I need to decide if I want to trade off the better weather on the coast for the waterfalls in Yosemite. Of course going in September will also guarantee us access to Glacier point which is also a plus.

Is anytime in September a good bet for the best weather, or should we wait until towards the end of the month?

Johnnyman, just how warm are you talking about for September weather?

I would wait until after Labor Day. Most kids go back to school on the day after Labor Day (at least here in So Cal), so Yosemite should be alot less crowded. Trust me, Yosemite Valley gets crowded beyond belief....

September is usually the third-warmest month here in Cali (at least for LA and Yosemite). It can be really warm (I think this last year, we had a heat wave the first week of September and it was 100 down here in So Cal). Here's the decision you have to make regarding the weather: the coast is probably at its best in late August - mid September, but that can be really hot for Yosemite Valley. Wait much longer though, and the coast gets cold. But, the coast is usually socked in with clouds from May - July 4th or so, so early summer really isnt a good option either. I say go anytime in September after labor day but before mid-October. You should be fine.

With the open jaw ticket you will have a drop fee for the one way rental car. Not huge but something to factor into your thinking.

I agree September is a better choice than May due to the iffy coastal weather. The coast between Monterey and Hearst Castle really is spectacular. You could hit a heat wave but then stay on the coast where it is cooler and as for Yosemite it is high enough that it will cool at night. You are coming from an area with much greater temperature extremes and think you will find the California weather very mild.